The invention relates to a method of manufacturing a welding stud from a wire by cold-working and by hardening and tempering, wherein the welding stud particularly serves to be welded to a workpiece by means of an electric stud welding method and consists of a mounting portion and a welding portion.
The present application claims priority to German Patent Application No. 100 14 078.5-14 filed Mar. 22, 2000.
The prior art already includes welding studs of this kind which, after they have been welded to a workpiece, serve for mounting or attaching objects, which purpose is fulfilled by the mounting portion of the welding stud.
Thus, this mounting portion has to have a higher strength than that of the welding portion.
The generally known prior art includes what is referred to as xe2x80x9cduo-threaded studsxe2x80x9d, which consist of two different materials in order to meet the above-mentioned requirements. Because of the different materials, it is time-consuming and expensive to manufacture these welding studs.
Furthermore, it is known to manufacture welding studs in such a way that the starting material, e.g. a wire, is first cold-worked and the welding stud thus manufactured is then hardened and tempered. This hardening and tempering is prescribed in standards for some property classes (relating to strength), e.g. property class 8.8.
As a result of hardening and tempering, however, high hardness peaks are disadvantageously created in the welding portion. Furthermore, a high welding current is required, which disadvantageously leads to spatter formation and thus to an uneven welding surface.
Accordingly, the object of the present invention is to provide a welding stud and a method of manufacturing the same with which the above-mentioned disadvantages are avoided and which makes a cost-efficient manufacture of the welding stud, which has a simple structure, possible.
According to the invention, this object is achieved by previously hardening and tempering the wire and subsequently cold-working it in such a way that the mounting portion and the welding portion have different strengths. This leads to the advantage that hardening and tempering is not effected on the stud itself but on the starting material. With the combination of the hardened and tempered starting material and the subsequent cold-working, the prescribed or desired property class (e.g. 8.8) is easily achieved.
In a further embodiment of the invention, as a result of cold-working, the mounting portion has a higher strength than the welding portion. Here, the diameter of the wire is reduced to a greater extent in the area of the mounting portion than in the area of the welding portion. Preferably, the reduction of the diameter of the wire may range from 40 to 60% in the area of the mounting portion and from 15 to 25% in the area of the welding portion. As starting material, a wire made of a hardened and tempered material, e.g. steel (St.37-3, 1.4301, 1.4571), may be used.
Alternatively, in a welding stud, particularly for welding to a workpiece by means of an electric stud welding method, comprising a welding portion and a stud end to be welded to the workpiece and a mounting portion for connection with an object. The invention proposes to manufacture the two portions consisting of the same material by cold-working, after the starring material has been pre-treated by hardening and tempering, in such a way that the portions have different strengths, preferably in such a way that the mounting portion has a higher strength than the welding portion. Alternatively, the starting material may be non-heat treated, microalloyed materials.